Experimental and theoretical study on piezoresistive properties of a structural resin reinforced with carbon nanotubes for strain sensing and damage monitoring

The development of embedded sensors based on a structural thermosetting epoxy resin reinforced with 0.3 wt% of multi-walled (MW) carbon nanotubes (CNTs) for real-time structural health monitoring is presented. The storage modulus of the composites is higher than 2000 MPa in a wide temperature range confirming their reliability as structural parts, especially for aeronautical applications. The piezoresistive properties are studied on specimens subjected to both tension and flexural stresses. The yield strength evaluated with the same approach adopted for metallic materials and alloys compares successfully with the information provided by the electrical characterization. Different levels of damages are revealed by the changes in the piezoresistive properties due to the morphological modifications in the conductive network of CNTs within the resin. The analysis of an empirical law is proposed for predicting the strain-dependence of the electrical and mechanical properties of material when the samples are subjected to stretch-release cycles. The average CNTs interparticle distances as function of bending is also estimated.